Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/vanetza/security/v2/subject_info.hpp

@@ -0,0 +1,58 @@
+#ifndef SUBJECT_INFO_HPP_WCKSWSKY
+#define SUBJECT_INFO_HPP_WCKSWSKY
+
+#include <vanetza/security/v2/serialization.hpp>
+#include <vanetza/common/byte_buffer.hpp>
+#include <array>
+#include <cstdint>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/// described in TS 103 097 v1.2.1, section 6.3
+enum class SubjectType : uint8_t
+{
+    Enrollment_Credential = 0,
+    Authorization_Ticket = 1,
+    Authorization_Authority = 2,
+    Enrollment_Authority = 3,
+    Root_CA = 4,
+    CRL_Signer = 5
+};
+
+/// described in TS 103 097 v1.2.1, section 6.2
+struct SubjectInfo
+{
+    SubjectType subject_type;
+    ByteBuffer subject_name;
+};
+
+/**
+ * \brief Serializes a SubjectInfo into a binary archive
+ */
+void serialize(OutputArchive&, const SubjectInfo&);
+
+/**
+ * \brief Deserializes a SubjectInfo from a binary archive
+ * \param archive with a serialized SubjectInfo at the beginning
+ * \param SubjectInfo
+ * \return size of the deserialized SubjectInfo
+ */
+size_t deserialize(InputArchive&, SubjectInfo&);
+
+/**
+ * \brief Calculates size of a SubjectInfo
+ * \param SubjectInfo
+ * \return number of octets needed to serialize SubjectInfo
+ */
+size_t get_size(const SubjectInfo&);
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* SUBJECT_INFO_HPP_WCKSWSKY */